Device for manufacturing oriented carbon nanotube aggregates

ABSTRACT

An apparatus for producing an aligned carbon nanotube includes: at least one injection section including at least one injection hole from which a raw material gas is injected to a base substrate; an exhaust vent for exhausting the raw material gas; and an exhaust section including a plurality of exhaust vents, the plurality of exhaust vents being provided so as to be closer to the exhaust vent than a plurality of injection holes included in the at least one injection hole of the at least one injection section.

This is a Division of application Ser. No. 14/236,133 filed Jan. 30,2014, which in turn is a national stage entry of PCT/JP2012/071313 filedAug. 23, 2012, which claims priority to JP 2011-183130 filed Aug. 24,2011. The disclosure of the prior applications is hereby incorporated byreference herein in its entirety.

TECHNICAL FIELD

The present invention relates to an apparatus for producing an alignedcarbon nanotube aggregate and a method for producing the aligned carbonnanotube aggregate.

BACKGROUND ART

Various techniques for producing a carbon nanotube (hereinafter referredto as “CNT”) aggregate have been reported.

Patent Literature 1 and Non-patent Literature 1 describe methods forproducing CNTs with use of a CVD method.

Patent Literature 2 describes a CNT production apparatus in which adirection in which a raw material gas is injected is adjusted to adirection in which CNTs grown from a metal catalyst film are aligned.

Patent Literature 3 describes an apparatus for producing an aligned CNTaggregate, the apparatus including (i) a seal gas injection sectionwhich injects a seal gas along an aperture plane of a growth furnacethrough which aperture plane a base substrate is taken out of the growthfurnace and (ii) an exhaust section which exhausts air so as to preventthe seal gas from entering the growth furnace.

Patent Literature 4 describes a CNT production method which is intendedto uniformly produce CNTs on a large area base substrate.

Patent Literature 5 describes a CNT production method which is intendedto cause CNTs to have a long fiber length without inhibiting supply of araw material gas to a catalyst supporting surface.

CITATION LIST Patent Literatures

-   Patent Literature 1-   Pamphlet of International Publication, No. WO 2009/128349-   Patent Literature 2-   Pamphlet of International Publication, No. WO 2008/096699-   Patent Literature 3-   Pamphlet of International Publication, No. WO 2011/001969-   Patent Literature 4-   Japanese Patent Application Publication, Tokukai, No. 2008-137831 A-   Patent Literature 5-   Japanese Patent Application Publication, Tokukai, No. 2007-126318 A

Non-Patent Literature

-   Non-patent Literature 1-   Kenji Hata et al., Water-Assisted Highly Efficient Synthesis of    Impurity-Free Single-Walled Carbon Nanotubes, SCIENCE, Nov. 19,    2004, Vol. 306, pp. 1362-1364

SUMMARY OF INVENTION Technical Problem

However, according to the conventional techniques, there occurs aproblem such that a base substrate which has such a large area as tohave a side length of 10 cm or larger causes a deterioration in qualityof CNTs to be obtained in a rim of the base substrate.

The present invention, which has been made in view of the above problem,provides an apparatus for producing an aligned CNT aggregate and amethod for producing the aligned CNT aggregate, the apparatus and themethod each capable of preventing a deterioration in quality of thealigned CNT aggregate in a rim of a base substrate even in a case wherea large area base substrate is used as the base substrate.

Solution to Problem

Inventors of the present invention expect that concentration unevennessof a raw material gas occurs on a base substrate due to the followingtwo reasons and the occurrence of the concentration unevenness causes adeterioration in quality of CNTs in a rim of the base substrate. Notethat, in a case where a catalyst activation material as well as the rawmaterial gas is supplied to the base substrate, concentration unevennessof the catalyst activation material is also expected to occur.

1: A difference in gas flow velocity increases from a center towards therim of the base substrate in proportion to an area of the basesubstrate.2: A raw material gas and/or a catalyst activation material (residualgas) which have/has been consumed at the center of the base substrate insynthesizing the CNTs and consequently have/has a lower concentrationflow towards the rim of the base substrate while flowing in a spacebetween the base substrate and an injection hole(s).

The inventors of the present invention made the following findings: (i)that, in a case where a plurality of exhaust vents are provided behindinjection holes of an injection section (shower) that injects a rawmaterial gas and/or a catalyst activation material, it is possible toexhaust a residual gas out of a furnace fast by preventing, as much aspossible, a flow of the residual gas in a space between a base substrateand the injection holes and (ii) that the fast exhaust of the residualgas allows a gas composition and a gas flow velocity to be more uniformon the entire surface of the base substrate, so that CNTs having moreuniform quality can be synthesized on a large area base substrate. Basedon the findings, the inventors accomplished the present invention.

That is, an apparatus of the present invention for producing an alignedcarbon nanotube aggregate is an apparatus for producing an alignedcarbon nanotube aggregate by synthesizing the aligned carbon nanotubeaggregate on a base substrate that supports a catalyst on a surfacethereof, the apparatus including: a growth unit for synthesizing thealigned carbon nanotube aggregate on the base substrate by supplying araw material gas for carbon nanotubes to the catalyst and heating atleast either the catalyst or the raw material gas, the growth unitincluding: at least one injection section including at least oneinjection hole from which the raw material gas is injected to the basesubstrate; a first exhaust vent being on one side, relative to the atleast one injection section, while a mounting surface on which the basesubstrate is placed is on the other side relative to the injectionsection, for exhausting, out of a growth furnace, the raw material gasthat was injected from the at least one injection hole and thencontacted the base substrate, the growth furnace storing the basesubstrate while the aligned carbon nanotube aggregate is beingsynthesized; and an exhaust section including a plurality of secondexhaust vents that exhausts, towards the first exhaust vent, the rawmaterial gas that contacted the base substrate, the plurality of secondexhaust vents being provided so as to be closer to the first exhaustvent than a plurality of injection holes included in the at least oneinjection hole of the at least one injection section.

Further, a method of the present invention for producing an alignedcarbon nanotube aggregate is a method for producing an aligned carbonnanotube aggregate by synthesizing the aligned carbon nanotube aggregateon a base substrate that supports a catalyst on a surface thereof, themethod including: a growth step of synthesizing the aligned carbonnanotube aggregate on the base substrate by supplying a raw material gasfor carbon nanotubes to the catalyst and heating at least either thecatalyst or the raw material gas, the growth step being carried out by agrowth unit, the growth unit including: at least one injection sectionincluding at least one injection hole from which the raw material gas isinjected to the base substrate; a first exhaust vent being on one side,relative to the at least one injection section, while a mounting surfaceon which the base substrate is placed is on the other side relative tothe injection section, for exhausting, out of a growth furnace, the rawmaterial gas that was injected from the at least one injection hole andthen contacted the base substrate, the growth furnace storing the basesubstrate while the aligned carbon nanotube aggregate is beingsynthesized; and an exhaust section including a plurality of secondexhaust vents that exhausts, towards the first exhaust vent, the rawmaterial gas that contacted the base substrate, the plurality of secondexhaust vents being provided so as to be closer to the first exhaustvent than a plurality of injection holes included in the at least oneinjection hole of the at least one injection section.

According to the configuration, the plurality of second exhaust ventsremove a residual gas from a space between the base substrate and theinjection holes before exhausting the residual gas from the entiregrowth unit. The residual gas is a residual substance of the rawmaterial gas or the raw material gas and a catalyst activation materialwhich is/are obtained after being supplied to the base substrate andused for synthesizing CNTs. Therefore, the residual gas has a lowerconcentration than the raw material gas supplied from the injectionholes. Further, in a case where the raw material gas includes thecatalyst activation material, the catalyst activation material also hasa lower concentration. According to the configuration, such a residualgas does not remain in the space between the base substrate and theinjection holes. Therefore, the raw material gas to be supplied to thebase substrate has a more uniform concentration. Further, in a casewhere the catalyst activation material is also supplied, the catalystactivation material also has a more uniform concentration. This canprevent a deterioration in quality of CNTs in a rim of the basesubstrate even in a case where a large area substrate is used as thebase substrate.

Advantageous Effects of Invention

According to the present invention, it is possible to bring about aneffect of providing an apparatus for producing an aligned CNT aggregatewhich apparatus is capable of preventing a deterioration in quality ofthe aligned CNT aggregate in a rim of a base substrate even in a casewhere a large area base substrate is used as the base substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view schematically showing a configuration of a growth unitof an aligned CNT aggregate production apparatus in accordance withEmbodiment 1 of the present invention.

FIG. 2 is a view schematically showing how a raw material gas flows inthe growth unit of Embodiment 1.

FIG. 3 is a view schematically showing a configuration of a growth unitof an aligned CNT aggregate production apparatus in accordance withEmbodiment 2 of the present invention.

FIG. 4 is a view schematically showing how a raw material gas flows inthe growth unit of Embodiment 2.

FIG. 5 is a view schematically showing a configuration of a growth unitof an aligned CNT aggregate production apparatus in accordance withEmbodiment 3 of the present invention.

FIG. 6 is a view schematically showing a configuration of a CNTproduction apparatus which is an embodiment of an aligned CNT aggregateproduction apparatus in accordance with the present invention.

FIG. 7 is a view showing a distribution of G/D ratios of an aligned CNTaggregate of Example 1′.

FIG. 8 is a graph showing the distribution of G/D ratios of the alignedCNT aggregate of Example 1.

FIG. 9 is a view showing a distribution of G/D ratios of an aligned CNTaggregate of Example 2.

FIG. 10 is a graph showing the distribution of G/D ratios of the alignedCNT aggregate of Example 2.

FIG. 11 is a view showing a distribution of G/D ratios of an aligned CNTaggregate of Example 3.

FIG. 12 is a graph showing the distribution of G/D ratios of the alignedCNT aggregate of Example 3.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention are specifically described below.

(Aligned CNT Aggregate)

First, the following description discusses an aligned CNT aggregateobtained from an aligned CNT aggregate production apparatus inaccordance with the present invention (hereinafter simply referred to asa “production apparatus of the present invention”).

An aligned CNT aggregate that is produced by a production apparatus ofthe present invention refers to a structure in which a large number ofCNTs having grown from a substrate are aligned along a particulardirection. A specific surface area of the aligned CNT aggregate when theCNTs are mostly unopened is preferably not less than 600 m²/g, and morepreferably not less than 800 m²/g. An aligned CNT aggregate having alarger specific surface area is preferable because such an aligned CNTaggregate can reduce an amount of impurities such as metals or carbonimpurities. A total amount of the impurities is preferably not more than40% of a CNT weight.

A weight density of the aligned CNT aggregate is preferably not lessthan 0.002 g/cm³ and not more than 0.2 g/cm³. In a case where the weightdensity is not more than 0.2 g/cm³, there will be a weakening in bindingof CNTs constituting the aligned CNT aggregate. Such a weakening rendersthe aligned CNT aggregate likely to be homogenously dispersed whenstirred into a solvent or the like. That is, a weight density of notmore than 0.2 g/cm³ makes it easy to obtain a homogenous dispersionliquid. Alternatively, a weight density of not less than 0.002 g/cm³leads to an improvement in the integrity of the aligned CNT aggregate.Such an improvement can prevent the aligned CNT aggregate from beingunbound, thus making it easy to handle the aligned CNT aggregate.

An aligned CNT aggregate which is aligned along a particular directionpreferably has a high degree of orientation. The high degree oforientation can be evaluated by at least any one of the following 1. to3.

1. In a case where the aligned CNT aggregate is irradiated with X raysfrom a first direction parallel with the longitudinal direction of theCNTs and from a second direction perpendicular to the first direction,and an x-ray diffraction intensity of the aligned CNT aggregate is thenmeasured (by θ-2θ method), a θ angle and a reflection direction where areflection intensity from the second direction is greater than that fromthe first direction are obtained. Further, a θ angle and a reflectiondirection where the reflection intensity from the first direction isgreater than that from the second direction are obtained.

2. In a case where an X-ray diffraction intensity is measured from atwo-dimensionally diffraction pattern image obtained by irradiating thealigned CNT aggregate with X rays from the direction perpendicular tothe longitudinal direction of the CNTs (by Laue method), a diffractionpeak pattern indicating presence of anisotropy appears.

3. A Herman's orientation factor calculated on the basis of the X-raydiffraction intensity obtained by θ-2θ method or Laue method is morethan 0 and less than 1, preferably not less than 0.25 and not more than1.

According to the X-ray diffraction method, (i) diffraction intensitiesof a (CP) diffraction peak and a (002) peak based on packing between thesingle-walled CNTs, and (ii) a diffraction peak intensity in a directionof X-rays that enter parallel and perpendicular to (100) and (110) peaksbased on a six-membered carbon ring constituting the single-walled CNTsare different from each other.

In order for an aligned CNT aggregate to exhibit orientation and a largespecific surface area, it is preferable that the height of the alignedCNT aggregate be in a range of not less than 10 μm and not more than 10cm. A height of not less than 10 μm leads to an improvement inorientation. Alternatively, a height of not more than 10 cm makes itpossible to improve the specific surface area, because such a heightmakes rapid generation possible and the adhesion of carbonaceousimpurities can therefore be controlled. Note that the “height” can beregarded as a length of the aligned CNT aggregate.

The aligned CNT aggregate preferably has a G/D ratio of not less than 3,and more preferably of not less than 4. The term “G/D ratio” means anindex that is commonly used to evaluate the quality of CNTs. A ramanspectrum of CNTs as measured by a raman spectroscopic instrument isobserved in vibration modes called “G band” (near 1,600 cm⁻¹) and “Dband” (near 1,350 cm⁻¹). The G band is a vibration mode derived fromhexagonal lattice structures of graphite appearing as cylindricalsurfaces of CNTs, and the D band is a vibration mode derived fromamorphous parts. Therefore, with a higher peak intensity ratio of the Gband to the D band (G/D ratio), the CNTs can be evaluated to be higherin crystallinity.

Embodiment 1

An embodiment of a growth unit included in a production apparatus of thepresent invention is described with reference to FIGS. 1 and 2. FIG. 1is a view schematically showing a configuration of a growth unit 10 ofan aligned CNT aggregate production apparatus in accordance withEmbodiment 1. FIG. 2 is a view schematically showing how a raw materialgas flows in the growth unit 10.

The growth unit 10 includes a growth furnace 11, an injection section12, and an exhaust section 13. The growth unit 10 further has an exhaustvent 15 (first exhaust vent) provided in an upper part thereof. Thegrowth unit 10 further includes a heater 16, which is described later.

The growth unit 10 is a set of devices for carrying out a growth step.The growth unit 10 has a function of, by carrying out the growth step,synthesizing an aligned CNT aggregate by (i) causing an environmentsurrounding a catalyst to be an environment of a raw material gas and(ii) heating at least either the catalyst or the raw material gas.

(Growth Step)

First, the following description discusses the growth step, which iscarried out by the growth unit included in the production apparatus ofthe present invention.

The growth step is a step of synthesizing an aligned CNT aggregate by(i) transferring a base substrate into a growth furnace, (ii) causing anenvironment surrounding a catalyst to be an environment of a rawmaterial gas in the growth furnace, and (iii) heating at least eitherthe catalyst or the raw material gas. That is, in the growth step, thealigned carbon nanotube aggregate is synthesized on the base substrateby, for example, a chemical vapor deposition (CVD) method.

For example, it is only necessary that in the growth step, the alignedCNT aggregate be synthesized on the base substrate by the CVD methodafter or while the raw material gas for a CNT is supplied to the growthfurnace into which the base substrate is being transferred.

It is more preferable that the growth step be carried out in thepresence of a catalyst activation material in an atmosphere in which theCNT growth reaction is carried out. The addition of the catalystactivation material makes it possible to further improve the efficiencyin the production of CNTs and the purity of the CNTs.

In the case of heating at least either the catalyst or the raw materialgas, it is more preferable to heat both the catalyst and the rawmaterial gas. It is only necessary that a temperature at which thecatalyst and/or the raw material gas allow CNTs to grow. The temperatureis preferably not less than 400° C. and not more than 1,100° C., and ismore preferably not less than 600° C. and not more than 900° C.Particularly in a case where the catalyst activation material is added,the temperature falling within the above range allows an effect of thecatalyst activation material to be expressed well and makes it possibleto prevent the catalyst activation material from reacting with CNT.

The growth step is carried out at a pressure preferably of not lowerthan 10² Pa and not higher than 10⁷ Pa (100 in atmospheric pressure), ormore preferably of not lower than 10⁴ Pa and not higher than 3×10⁵ Pa (3in atmospheric pressure).

(Raw Material Gas)

As a raw material gas, any substance that can be a raw material for CNTscan be used. For example, gases having raw-material carbon sources atthe growth temperature can be used. Among them, hydrocarbons such asmethane, ethane, ethylene, propane, butane, pentane, hexane, heptane,propylene, and acetylene are suitable. In addition, lower alcohols suchas methanol and ethanol, and mixtures thereof can be used. Further, theraw material gas may be diluted with an inert gas.

(Inert Gas)

The inert gas only needs to be a gas that is inert at the temperature atwhich CNTs grow, does not cause a decrease in activity of the catalyst,and does not react with the growing CNTs. Examples that can be given arehelium, argon, nitrogen, neon, krypton, and mixtures thereof. Inparticular, nitrogen, helium, argon, and mixtures thereof are suitable.

(Catalyst Activation Material)

It is more preferable that the growth step be carried out in thepresence of a catalyst activation material in an atmosphere in which theCNT growth reaction is carried out. The catalyst activation material ismore preferably an oxygen-containing substance, and is still morepreferably a substance that does no significant damage to CNTs at theCNT growth temperature. Effective examples include: water, oxygen,ozone, acidic gases, nitrogen oxide; low-carbon oxygen-containingcompounds such as carbon monoxide and carbon dioxide; alcohols such asethanol and methanol; ethers such as tetrahydrofuran; ketones such asacetone; aldehydes; esters; and mixtures of thereof. Among them, water,oxygen, carbon dioxide, carbon monoxide, and ethers are preferable. Inparticular, water and carbon dioxide are suitable.

The catalyst activation material is not particularly limited in amountto be added. However, when the catalyst activation material is water,the catalyst activation material only needs to be added in a rangepreferably of not less than 10 ppm and not more than 10,000 ppm, morepreferably of not less than 50 ppm and not more than 1,000 ppm, andstill more preferably of not less than 200 ppm and not more than 700ppm, in a concentration in an environment surrounding the catalyst.Further, carbon dioxide which is used as the catalyst activationmaterial has a concentration preferably of not less than 0.2% by volumeand not more than 70% by volume, more preferably of not less than 0.3%and not more than 50% by volume, and still more preferably of not lessthan 0.7% by volume and not more than 20% by volume.

The mechanism by which the catalyst activation material functions iscurrently supposed to be as follows: In the process of growth of CNTs,adhesion of by-products such as amorphous carbon and graphite to thecatalyst causes deactivation of the catalyst and the growth of CNTs istherefore inhibited. However, the presence of the catalyst activationmaterial causes amorphous carbon and graphite to be oxidized into carbonmonoxide, carbon dioxide, or the like and therefore gasified. Therefore,the catalyst activation material is believed to cleanse a catalyst layerand express a catalyst activation function, that is, a function ofenhancing the activity of the catalyst and extending the activelongevity of the catalyst.

Note that compounds containing carbon and oxygen such as alcohols andcarbon monoxide can act as both a raw material gas and a catalystactivation material. For example, it is expected the alcohols and thecompounds each containing carbon and oxygen act as catalyst activationmaterials when used in combination with a raw material gas that iseasily decomposed to be a carbon source (e.g., ethylene). Meanwhile, itis expected the alcohols and the compounds each containing carbon andoxygen act as raw material gases when used in combination with acatalyst activation material having a high activity (e.g., water).Furthermore, it is expected, in the case of, for example, carbonmonoxide, that carbon atoms which are generated by being decomposedserve as carbon sources of the CNT growth reaction, whereas oxygen atomsact as catalyst activation materials which gasify, by oxidization,amorphous carbon, graphite, and the like.

(High-Carbon-Concentration Environment)

It is preferable that a raw material gas atmosphere be ahigh-carbon-concentration environment. Specifically, thehigh-carbon-concentration environment is a growth atmosphere in whichthe proportion of the raw material gas to the total flow is preferably 2to 20%. Since the activity of the catalyst is remarkably improvedparticularly in the presence of the catalyst activation material, thecatalyst is not deactivated even in an environment of high-carbonconcentration. Thus, long-term growth of CNTs is made possible, and thegrowth rate is remarkably improved. However, in an environment ofhigh-carbon concentration, a large amount of carbon contaminants easilyadhere to a furnace wall and the like, as compared with an environmentof low-carbon concentration. According to the production apparatus ofthe present invention, it is possible to efficiently exhaust a residualgas. This allows the production apparatus of the present invention to beexcellent in productivity of the aligned CNT aggregate.

[Base Substrate 111]

Next, the following description discusses a base substrate 111 to beused in the growth step. The base substrate 111 is a substrate having abase substrate that supports thereon a catalyst for a growth reaction ofCNTs.

It is only necessary that a base substrate constituting the basesubstrate 111 be a member capable of supporting a catalyst for a CNTgrowth on a surface thereof. The base substrate can preferably maintainits shape even at a high temperature of not lower than 400° C. Examplesof materials usable for the base substrate include: metals such as iron,nickel, chromium, molybdenum, tungsten, titanium, aluminum, manganese,cobalt, copper, silver, gold, platinum, niobium, tantalum, lead, zinc,gallium, indium, germanium, and antimony; alloys and oxides containingthese metals; nonmetals such as silicon, quartz, glass, mica, graphite,and diamond; and ceramic. The metal materials, which are lower in costthan silicon and ceramic, are preferable. In particular, a Fe—Cr(iron-chromium) alloy, a Fe—Ni (iron-nickel) alloy, a Fe—Cr—Ni(iron-chromium-nickel) alloy, and the like are suitable.

The base substrate may take the form of a flat plate, a thin film, ablock, or the like. However, in particular, the form of the flat platein which form the base substrate has a large surface area for its volumeis advantageous to mass production.

In a case where the base substrate 111 which takes the form of a flatplate is used, the base substrate 111 is not particularly limited inthickness. For example, it is possible to use, as the base substrate111, a thin film having a thickness of approximately several μm toapproximately several centimeters. The thickness is preferably not lessthan 0.05 mm and not more than 3 mm. The thickness of not more than 3 mmallows the base substrate 111 to be sufficiently heated in a CVD step.This can prevent insufficient growth of the CNTs and reduce cost of thebase substrate 111. The thickness of not less than 0.05 mm preventsdeformation of the base substrate 111 due to carburizing and makes itdifficult for bending of the base substrate 111 itself to easily occur.This is advantageous in transferring and/or recycling the base substrate111. Note that the term carburizing herein refers to infiltration of acarbon component into the base substrate 111.

The base substrate which takes the form of a flat plate form is notparticularly limited in shape and size. However, it is possible to use,as the base substrate, a rectangular or square base substrate. The basesubstrate is not particularly limited in length of a side. However, aside having a longer length is more desirable in terms of massproductivity of CNTs. According to the present invention, a large-sizedbase substrate can be suitably used. For example, an aligned CNTaggregate can be produced more uniformly on a base substrate having aside of not less than 100 mm and not more than 1,000 mm.

(Carburizing Prevention Layer)

The base substrate 111 may have a carburizing prevention layer formed onat least either a front or back surface thereof. It is desirable thatthe base substrate 111 have a carburizing prevention layer formed oneach of the front and back surfaces thereof. The carburizing preventionlayer is a protecting layer for preventing the base substrate 111 frombeing carburized and therefore deformed in the step of generating carbonnanotubes.

It is preferable that the carburizing prevention layer be composed of ametal or ceramic material, or especially preferably the ceramicmaterial, which is highly effective in preventing carburizing. Examplesof the metal include copper and aluminum. Examples of the ceramicmaterial include: oxides such as aluminum oxide, silicon oxide,zirconium oxide, magnesium oxide, titanium oxide, silica alumina,chromium oxide, boron oxide, calcium oxide, and zinc oxide; and nitridessuch as aluminum nitride and silicon nitride. Among them, aluminum oxideand silicon oxide are preferable because they are highly effective inpreventing carburizing.

(Catalyst)

The base substrate 111 supports a catalyst. In a case where thecarburizing prevention layer is provided on the base substrate 111, thecarburizing prevention layer supports the catalyst thereon. Examples ofthe catalyst include iron, nickel, cobalt, molybdenum, a chloridethereof, an alloy thereof, and a complex or layer thereof with aluminum,alumina, titania, titanium nitride, or silicon oxide. Examples that canbe given are an iron-molybdenum thin film, an alumina-iron thin film, analumina-cobalt thin film, an alumina-iron-molybdenum thin film, analuminum-iron thin film, and an aluminum-iron-molybdenum thin film. Thecatalyst can be used in a range of existential quantities that is usablefor production of CNTs. For example, in the case of use of iron, it ispreferable that the thickness of a film formed be in a range of not lessthan 0.1 nm and not more than 100 nm, more preferably not less than 0.5nm and not more than 5 nm, or especially preferably not less than 0.8 nmand not more than 2 nm.

It is possible to apply either a wet or dry process to the formation ofthe catalyst onto the surface of the base substrate. Specifically, it ispossible to apply a sputtering evaporation method or a method forspreading/calcining a liquid obtained by dispersing fine metal particlesin an appropriate solvent. Further, it is possible to form the catalystinto any shape with concomitant use of patterning obtained by applyingwell-known photolithography, nanoprinting, or the like.

A production method of the present invention makes it possible toarbitrarily control the shape of an aligned CNT aggregate, according tothe catalyst patterning formed on the substrate and the growth time forCNTs, so that the aligned CNT aggregate takes a thin-film shape, acylindrical shape, a prismatic shape, or any other complicated shape. Inparticular, in the shape of a thin film, the aligned CNT aggregate hasan extremely small thickness as compared with its length and width;however, the length and width can be arbitrarily controlled according tothe catalyst patterning, and the thickness can be arbitrarily controlledaccording to the growth time for CNTs that constitute the aligned CNTaggregate. Note that the “thickness” can also be regarded as a height ofthe aligned CNT aggregate.

[Growth Furnace 11]

Next, the following description discusses members constituting the unit10. The growth furnace 11 is a furnace for (i) retaining an environmentof a raw material gas which environment surrounds a base substrate and(ii) storing the base substrate 111 while synthesizing an aligned carbonnanotube aggregate.

The growth furnace 11 has a bottom surface which serves as a mountingsurface 14 on which the base substrate 111 is placed. During the growthstep, the base substrate 111 is placed on the mounting surface 14.

The growth furnace 11 has the exhaust vent 15 provided in the upper partthereof. The exhaust vent 15 is on one side, relative to the injectionsection 12, while the mounting surface 14 on which the base substrate111 is placed is on the other side relative to the injection section 12.The exhaust vent 15 is provided for exhausting a raw material gas thatwas injected from injection holes 12 a and then contacted the basesubstrate 111. The raw material gas supplied from the injection section12 is exhausted from the growth furnace 11 through the exhaust vent 15via an exhaust section 13 (described later) in a direction indicated byan arrow X. It is possible to appropriately employ, as a mechanism forexhausting the raw material gas from the exhaust vent 15, a conventionalmethod for sucking the raw material gas by suction means such as a pump.

According to the present embodiment, the exhaust vent 15 is an openingwhich is provided on an inner wall of the growth furnace 11 andconnected to a pipe from which the raw material gas in the growthfurnace 11 is exhausted. According to the production apparatus of thepresent invention, the first exhaust vent is on one side, relative tothe injection section, while the mounting surface on which the basesubstrate is placed on the other side relative to the injection section.The first exhaust vent is an opening from which to exhaust a rawmaterial gas that was injected from injection holes and then contactedthe base substrate. According to the present embodiment, the opening isprovided on the inner wall of the growth furnace 11, and gas havingpassed through the opening is exhausted from the growth unit 10 throughthe pipe. However, configurations of the first exhaust vent and the pipeconnected to the first exhaust vent are not limited to those of thepresent embodiment. For example, the first exhaust vent and the pipeconnected to the first exhaust vent may be realized by a unit having thefollowing configuration. That is, the unit (i) has a surface thatcorresponds to the exhaust section 13 (described later) and (ii)protrudes in side view by being provided with a pipe opposed to exhaustvents 13 a. According to the unit having the configuration, an openingin which the pipe contacts a space containing gas having passed throughthe exhaust vents 13 a corresponds to the first exhaust vent. Theconfiguration makes it possible to easily obtain an advantage of thepresent invention by incorporating the unit into a conventional growthfurnace.

Further, a configuration of the pipe of the present embodiment, whichpipe has an end corresponding to the exhaust vent 15 and leads gashaving passed through the exhaust vent 15, is not limited to theconfiguration which is illustrated in FIG. 1 and in which the pipe isopposed to the mounting surface 14 relative to the injection section 12.For example, the pipe may be configured to collect, in the first exhaustvent, gas having passed through second exhaust vents, and then exhaustthe gas by inverting the pipe toward the mounting surface. In otherwords, according to the present embodiment, it is only necessary thatthe first exhaust vent be opposed to the mounting surface relative tothe injection section. Further, (i) the pipe which is connected to thefirst exhaust vent and (ii) the opening which is an outlet of the pipeand from which gas is finally exhausted from the growth unit do not needto be opposed to the mounting surface relative to the injection section.

Further, the growth furnace 11 may include a reaction gas injectionsection. Furthermore, the pipe for leading, to an outside of the growthunit 10, the gas having passed through the exhaust vent 15 can includean exhaust flow volume stabilization section. A reaction gas and theexhaust flow volume stabilization section are described later.

[Injection Section 12]

The injection section 12 supplies a raw material gas to the basesubstrate 111. The injection section 12 may also be used as necessary tosupply a catalyst activation material to the base substrate 111.

The injection section 12 includes pipes which are provided like a comb.The pipes are each provided with an injection hole row in which aplurality of injection holes 12 a are aligned. In a case where the pipeseach provided with the injection hole row are thus provided like a comb,it is possible to more uniformly supply a raw material gas and acatalyst activation material to the base substrate 111.

In a case where a base substrate which is 500 mm square is used as thebase substrate 111 and the growth furnace 11 has a height of 300 mm, itis more preferable that the injection section 12 be at a height of notless than 10 mm and not more than 100 mm above the mounting surface 14.

The injection holes 12 a are provided in a place facing a surface of thebase substrate 111 on which surface a catalyst is formed. The “placefacing” means a place in which an injection axis line of each of theinjection holes 12 a forms an angle of not less than 0° and less than90°, preferably of not less than 0° and not more than 60°, morepreferably of not less than 0° and not more than 30° with a line normalto the base substrate 111. That is, the flow direction of gas asinjected from the injection holes 12 a of the injection section 12 issubstantially orthogonal to the base substrate 111. The injectionsection 12 thus configured makes it possible to spray the raw materialgas uniformly onto a base substrate and therefore efficiently consumethe raw material gas. This makes it possible, as a result, to enhancethe uniformity of an aligned CNT aggregate that grows on the basesubstrate 111 and lower the consumption of the raw material gas.

The injection holes 12 a can have any shape such as a circular shape, atriangular shape, a quadrangular shape, a hexagonal shape, an ellipticalshape, or a cross shape. However, in terms of easiness of processing, itis preferable that the injection holes 12 a have a circular shape. It ismore preferable that the circular shape have a diameter of not shorterthan 0.1 mm and not longer than 10 mm. Further, in a case where a basesubstrate which is 500 mm square is used as the base substrate of thepresent invention, it is preferable that not less than 3 and not morethan 300 injection holes 12 a be provided for each injection hole row.Further, it is preferable that not less than 3 and not more than 300injection hole rows be provided at regular intervals.

[Exhaust Section 13]

The exhaust section 13 is provided between the injection section 12 andthe exhaust vent 15. The exhaust section 13 is a member having a surfaceon which the exhaust vents 13 a (second exhaust vents) are provided forexhausting, towards the exhaust vent 15, a raw material gas havingcontacted the base substrate 111.

The exhaust section 13 is provided so as to be closer to the exhaustvent 15 than the injection holes 12 a. That is, all of the exhaust vents13 a are provided so as to be closer to the exhaust vent 15 than all ofthe injection holes 12 a.

The second exhaust vents which are thus provided so as to be closer tothe first exhaust vent than the injection holes remove a residual gasfrom a space between the base substrate and the injection holes beforeexhausting the residual gas from the entire growth unit. This preventsthe residual gas from remaining in the space between the base substrateand the injection holes, so that a raw material gas and/or a catalystactivation material are/is supplied to the base substrate at a moreuniform concentration(s). This can prevent a deterioration in quality ofCNTs in a rim of the base substrate even in a case where a large areabase substrate is used as the base substrate.

Without the exhaust section 13, the residual gas would remain anddiffuse in the growth furnace 11. That is, the residual gas, which isobtained after a raw material and a catalyst activation material areused on a surface of the base substrate 111 and has a reducedconcentration, remains and diffuses, so that the raw material and thecatalyst activation material have respective less uniform concentrationsin the growth furnace 11. However, in a case where the exhaust section13 is provided in a space between the injection section 12 and theexhaust vent 15, it is possible to further reduce a region in which gasobtained after the raw material and the catalyst activation materialwere used on the surface of the base substrate 111 diffuses, andconsequently to cause the raw material gas and the catalyst activationmaterial to have respective more uniform concentrations in a spacebetween the injection section 12 and the base substrate 111.

The exhaust section 13 has a plate-like structure having a surfacefacing the mounting surface 14 on which the base substrate 111 isplaced. The surface is provided with the exhaust vents 13 a. The exhaustsection 13 having the surface forms a space between the base substrate111 and the surface. It goes without saying that the space is smallerthan the entire inner space of the growth furnace 11 in the case of theexhaust section 13 having no surface. This reduces a region in which theresidual gas remains and diffuses. The residual gas is exhausted fastfrom the reduced region. This allows the raw material gas etc. to have amore uniform concentration(s) in the space between the base substrate111 and the injection section 12.

In a case where a base substrate which is 500 mm square is used as thebase substrate 111 and the growth furnace 11 has a height of 300 mm, itis more preferable that the exhaust section 13 be provided at a heightof not less than 10 mm and not more than 200 mm above the mountingsurface 14. The exhaust section 13 which has a higher height causes theraw material gas and the catalyst activation material to be exhaustedfrom the space between the injection section 12 and the base substrate111 more slowly. This causes the raw material gas and the catalystactivation material to remain in the space for a longer time andconsequently causes the raw material gas and the catalyst activationmaterial to be used in larger amounts, so that the raw material gas andthe catalyst activation material are less lost. However, from theviewpoint of further uniformization of respective concentrations of theraw material gas and the catalyst activation material in the space, itis more preferable that the exhaust section 13 have a lower height.Therefore, the above-mentioned range is more suitable.

Further, at least one of exhaust vent rows in which the exhaust vents 13a are aligned is located between adjacent ones of the pipes constitutinga comb-like pattern of the injection section 12. That is, an exhaustvent row is provided between adjacent injection hole rows. Such anarrangement causes the injection holes 12 a and the exhaust vents 13 ato be close to each other. This allows faster exhaust from the exhaustvents 13 a of a residual gas obtained after a raw material gas injectedfrom the injection holes 12 a is supplied to the base substrate 111 andthen reflected from the base substrate. Therefore, it is possible tomore efficiently prevent the residual gas from remaining in the spacebetween the base substrate 111 and the injection holes 12 a, so that theraw material gas to be supplied to the base substrate 111 has a moreuniform concentration. Further, in a case where a catalyst activationmaterial is also supplied, the catalyst activation material also has amore uniform concentration. Note that the exhaust vents 13 a do not needto be provided in a place between respective rows of the injection holes12 a. The exhaust vents 13 a can be provided in a place other than theabove-mentioned space. For example, the exhaust vents 13 a can beprovided on the entire surface facing the mounting surface 14.

The exhaust vents 13 a can have any shape such as a circular shape, atriangular shape, a quadrangular shape, a hexagonal shape, an ellipticalshape, or a cross shape. However, in terms of easiness of processing, itis preferable that the exhaust vents 13 a have a circular shape. It ismore preferable that the circular shape have a diameter of not shorterthan 1 mm and not longer than 60 mm. It is preferable that the exhaustvents be provided so as to have an aperture ratio of not less than 1%and not more than 60% to the surface facing the mounting surface 14.Further, in a case where a base substrate which is 500 mm square is usedas the base substrate of the present invention, it is preferable thatnot less than 2 and not more than 300 exhaust vents be provided for eachexhaust vent row. Further, it is preferable that not less than 2 and notmore than 300 exhaust vent rows be provided in a space between therespective injection hole rows at regular intervals.

(Flow of Raw Material Gas)

Next, the following description discusses, with reference to FIG. 2, howa raw material gas flows in the growth unit 10.

A raw material gas is injected from the injection holes 12 a towards thebase substrate 111 in a direction indicated by an arrow a. The rawmaterial gas thus injected flows along a surface of the base substrate111 in directions indicated by arrows b. In this case, if the rawmaterial gas continues flowing along the directions indicated by thearrows b, the raw material gas having a reduced concentration contacts acatalyst in a rim of the base substrate 111. This causes a deteriorationin quality of CNTs that grow in the rim of the base substrate 111.

However, according to the present embodiment, the flow of the residualgas in a space between the injection holes 12 a and the base substrate111 is prevented by, for example, sucking, from the exhaust vents 13 a,the raw material gas which remains in the space. That is, the rawmaterial gas supplied to the base substrate 111 flows in a directionindicated by an arrow c and moves in a direction indicated by an arrow dso as to be exhausted from the exhaust vents 13 a.

This allows a composition and a flow velocity of the raw material gas tobe more uniform on the entire surface of the base substrate 111, so thatan aligned CNT aggregate with more uniform quality can be synthesized onthe base substrate 111 which has a large area.

(Section to Add a Catalyst Activation Material)

As described earlier, it is more preferable that the growth step becarried out in the presence of a catalyst activation material in anatmosphere in which the CNT growth reaction is carried out. For thisreason, the growth unit 10 includes a section to add a catalystactivation material (not illustrated). The section to add a catalystactivation material is a set of devices for either adding a catalystactivation material into a raw material gas, or adding a catalystactivation material directly to an environment surrounding the catalystinside of the growth unit 10. Means for supplying the catalystactivation material is not particularly limited. Examples of the meansinclude supplying the catalyst activation material through a bubbler,supplying the catalyst activation material by vaporizing a solutioncontaining the catalyst activation material, supplying the catalystactivation material as it is in a gaseous state, and supplying thecatalyst activation material by liquefying/vaporizing a solid catalystactivation material. It is possible to build a supply system usingvarious apparatuses such as a vaporizer, a mixer, a stirrer, a diluter,a sprayer, a pump, and a compressor. Furthermore, it is possible toprovide a tube for the supply of the catalyst activation material with adevice for measuring the concentration of the catalyst activationmaterial. Through feedback control using values outputted from themeasuring device, stable supply of the catalyst activation material witha small number of changes over time can be ensured.

Also for an injection section for injecting the catalyst activationmaterial, it is possible to use an injection section having aconfiguration similar to that of the injection section 12 for injectingthe raw material gas. Use of such an injection section makes it possibleto spray the catalyst activation material uniformly onto the basesubstrate 111, and therefore enhance the activity of the catalyst andextend the longevity of the catalyst. This allows aligned CNT aggregatesto continue to grow over a long period of time. The catalyst activationmaterial may be added to the raw material gas and injected, togetherwith the raw material gas, from the injection section 12. A similareffect can also be obtained in this case.

Embodiment 2

Next, a second embodiment of a growth unit included in a productionapparatus of the present invention is described with reference to FIGS.3 and 4. FIG. 3 is a view schematically showing a configuration of agrowth unit 20 of an aligned CNT aggregate production apparatus inaccordance with Embodiment 2. FIG. 4 is a view schematically showing howa raw material gas flows in the growth unit 20. Note that, forconvenience of description, members having functions identical to thoseof the respective members illustrated in the drawings of Embodiment 1are given respective identical reference numerals, and a description ofthose members is omitted here. Note also that the present embodimentmainly describes a point(s) of difference from Embodiment 1.

As shown in FIGS. 3 and 4, the growth unit 20 is made of a member ofwhich the growth unit 10 is made. However, a difference in location ofan exhaust section 13 of Embodiment 2 from the exhaust section 13 ofEmbodiment 1 forms a gap A. More specifically, since the growth unit 20is arranged such that the exhaust section 13 is provided so as to beupper than pipes of an injection section 12, i.e., the exhaust section13 is closer to an exhaust vent 15, the gap A is provided between therespective pipes each provided with an injection hole row.

As shown in FIG. 4, a residual gas obtained after a raw material gasinjected from injection holes 12 a is supplied to a base substrate 111and then reflected from the base substrate 111 passes through the gap Afast and is removed from a space between the base substrate 111 and theinjection holes 12 a. That is, the gap A serves as a path through whichthe residual gas passes so as to be removed from the space. Therefore,it is possible to more efficiently prevent the residual gas fromremaining in the space between the base substrate 111 and the injectionholes 12 a, so that the raw material gas to be supplied to the basesubstrate has a more uniform concentration. Further, in a case where acatalyst activation material is also supplied, the catalyst activationmaterial also has a more uniform concentration.

Embodiment 3

Next, a third embodiment of a growth unit included in a productionapparatus of the present invention is described with reference to FIG.5. FIG. 5 is a view schematically showing a configuration of a growthunit 30 in Embodiment 3. Note that, for convenience of description,members having functions identical to those of the respective membersillustrated in the drawings of Embodiment 1 are given respectiveidentical reference numerals, and a description of those members isomitted here. Note also that the present embodiment mainly describes apoint(s) of difference from Embodiment 1.

The growth unit 30 is different from those of Embodiments 1 and 2 inthat the growth unit 30 includes two injection sections, which are aninjection section 32′ and an injection section 32″.

More specifically, the growth unit 30 includes the injection section 32′and the injection section 32″. The injection section 32′ and theinjection section 32″″ face each other so that a comb tooth of one ofthe injection sections is located between respective comb teeth of theother of the injection sections.

A raw material gas is supplied from respective opposite directionsindicated by arrows A and B. The raw material gas is heated to have ahigher temperature while passing through pipes. However, in a placewhere the raw material gas supplied from the direction indicated by thearrow A is high in temperature, the raw material gas supplied from thedirection indicated by the arrow B is heated for a short time and thusremains low in temperature. Therefore, since the injection section 32′and the injection section 32″ face each other so that a comb tooth ofone of the injection sections is located between respective comb teethof the other of the injection sections, it is possible to uniformize atemperature distribution in a width direction of a base substrate 111.

The present embodiment thus makes it possible to further preventunevenness in temperature and heating history of a raw material gas andconsequently to supply, to a base substrate, the raw material gas whichis more uniform in temperature and heating history. Therefore, it ispossible to produce CNTs with more uniform quality.

In terms of prevention of unevenness in temperature of a raw materialgas, the growth unit 30 is more preferable than the growth unit 10 andthe growth unit 20.

Example of Production Apparatus of Present Invention

Next, the following description discusses an example of a productionapparatus of the present invention with reference to FIG. 6. FIG. 6 is aview showing a configuration of a CNT production apparatus 100, which isan embodiment of an aligned CNT aggregate apparatus in accordance withthe present invention. This section discusses an example of a CNTproduction apparatus including the growth unit 10 described as thegrowth unit in Embodiment 1.

The CNT production apparatus 100 includes an inlet purge section 101, aformation unit 102, gas mixing prevention means 103, a growth unit 10, acooling unit 105, an outlet purge section 106, a transfer unit (transfermeans) 107, and connecting sections 108 through 110.

The formation unit 102, the growth unit 10, and the cooling unit 105include a formation furnace 102 a, a growth furnace 11, and a coolingfurnace 105 a, respectively. Respective furnace spaces of the formationfurnace 102 a, the growth furnace 11, and the cooling furnace 105 a arespatially connected via the connecting sections 108 through 110.

[Inlet Purge Section 101]

The inlet purge section 101 is provided at an inlet of the productionapparatus 100. The inlet purge section 101 is a set of devices forpreventing the outside air from flowing into a furnace of the apparatusthrough an inlet for a base substrate 111. The inlet purge section 101has such a function that an environment surrounding the base substrate111 transferred into the apparatus is replaced by a purge gas.

The inlet purge section 101 has a gas curtain structure in which thepurge gas is injected from up and down in the form of a shower. Thisprevents the outside air from flowing in the production apparatus 100through the inlet of the apparatus. The inlet purge section 101 may beconstituted by, for example, a furnace or a chamber in which the purgegas is retained and a gas injection section for injecting the purge gas.

It is preferable that the purge gas be an inert gas. In particular, interms of safety, cost, and purging properties, it is preferable that thepurge gas be nitrogen.

In a case where the inlet for the base substrate 111 is always open,e.g., in a case where the transfer unit 107 is of a belt-conveyor typeas in the present embodiment, it is preferable that the inlet purgesection 101 have the gas curtain structure as described above. Thisconfiguration makes it possible to prevent the outside air from flowinginto the production apparatus 100 through the inlet for the basesubstrate 111.

[Formation Unit 102]

The formation unit 102 is a set of devices for realizing a formationstep. The formation unit 102 has a function of causing an environmentsurrounding a catalyst formed on a surface of the base substrate 111 tobe an environment of a reducing gas and heating at least either thecatalyst or the reducing gas.

The formation unit 102 is constituted by the formation furnace 102 a inwhich the reducing gas is retained, an injection section 102 b forinjecting the reducing gas into the formation furnace 102 a, and aheater 102 c for heating at least either the catalyst or the reducinggas.

It is possible to use, as the injection section 102 b, a shower headincluding a plurality of injection holes. The injection section 102 bhaving the configuration is provided in a place facing a surface of thebase substrate 111 on which surface a catalyst is formed. The “placefacing” means a place in which an injection axis line of each of theinjection holes forms an angle of not less than 0 and less than 90° witha line normal to the base substrate 111. That is, the flow direction ofgas as injected from the injection holes of the injection section 102 bis substantially orthogonal to the base substrate 111.

Use of such a shower head as the injection section 102 b makes itpossible to spray the reducing gas uniformly onto the base substrate 111and therefore efficiently reduce the catalyst. This makes it possible,as a result, to enhance the uniformity of an aligned CNT aggregate thatgrows on the base substrate 111 and lower the consumption of thereducing gas.

A heater used as the heater 102 c is not limited provided that it iscapable of heating, and examples of such a heater include a resistanceheating heater, an infrared heating heater, and an electromagneticinduction heater. It is preferable that the heating temperature be in arange of 400° C. to 1,100° C.

(Reducing Gas)

In general, a reducing gas is a gas that has at least one of the effectsof reducing a catalyst, stimulating the catalyst to become fineparticles suitable for the growth of CNTs, and improving the activity ofthe catalyst, and that is in a gaseous state. Examples of the reducinggas include hydrogen gas, ammonium, water vapor, or a mixture thereof.Alternatively, it is possible to apply a mixed gas obtained by mixingsuch a gas with an inert gas such as helium gas, argon gas, or nitrogengas. The reducing gas is generally used in a formation step, however,the reducing gas may be used in a growth step as appropriate.

(Formation Step)

The formation step is a step of causing an environment surrounding thecatalyst supported on the base substrate 111 to be an environment of thereducing gas and heating the catalyst and/or the reducing gas. This stepbrings about at least one of the effects of reducing the catalyst,stimulating the catalyst to become fine particles suitable for thegrowth of CNTs, and improving the activity of the catalyst.

The catalyst and/or the reducing gas preferably have/has a temperatureof not lower than 400° C. and not higher than 1,100° C. during theformation step. Further, the formation step is preferably carried outfor a time being not shorter than 3 minutes and not longer than 30minutes, and more preferably not shorter than 3 minutes and not longerthan 8 minutes. In a case where the formation step is carried out for atime falling within the above range, fine catalyst particles areprevented from being rough. This can prevent generation of multiwallcarbon nanotubes during the growth step.

For example, in a case where iron is used as the catalyst, a ferrichydroxide thin film or an iron oxide thin film is formed on the basesubstrate 111, the iron is reduced and micronized concurrently with orafter the formation of the ferric hydroxide thin film or the iron oxidethin film, so that fine iron particles are formed. Further, in a casewhere the carburizing prevention layer provided on the base substrate111 is made of alumina and a catalyst metal is iron, the iron catalystlayer is reduced to become fine particles, whereby a large number offine iron particles in nanometer size are formed on the alumina layer.Thus, the catalyst is prepared to be a catalyst suitable to productionof aligned CNT aggregates.

[Growth Unit 10]

The growth unit 10 of the present embodiment is identical to thatdescribed in Embodiment 1. Note that FIG. 6 illustrates a heater 16included in the growth unit 10.

Here, the heater 16 is described. The heater 16 is not limited providedthat it is capable of heating, and examples of such a heater include aresistance heating heater, an infrared heating heater, and anelectromagnetic induction heater. It is preferable that the heatingtemperature be in a range of 400° C. to 1,100° C.

[Reaction Gas]

It is preferable that a reaction gas be used in the present invention.The reaction gas reduces a carbon solid that adheres to an inside of apipe for leading, to an outside of the growth unit 10, gas having passedthrough an exhaust vent 15. The reaction gas has a function of changinga residual gas to a lower alkane, carbon monoxide, or carbon dioxide soas to prevent generation of a carbon solid that adheres to the inside ofthe pipe. The reaction gas preferably contains hydrogen atoms and/oroxygen atoms, whose specific examples include hydrogen, ammonia, oxygen,ozone, and water vapor. The reaction gas is preferably hydrogen oroxygen in terms of easiness of handling and greatness of a carbon solidgeneration prevention effect. In order to efficiently facilitate achemical reaction of the residual gas and the reaction gas, it ispossible to, for example, maintain a mixture of the residual gas and thereaction gas at a high temperature, cause the reaction gas to have ahigh concentration, and use a metal catalyst. In a case where themixture of the residual gas and the reaction gas is maintained at a hightemperature, such a temperature is preferably 400° C. or higher, andmore preferably 600° C. or higher. It is only necessary that an amountof the reaction gas to be supplied to the residual gas be controlled sothat the reaction gas has a concentration, as a volume fraction(calculated in a standard state) of, for example, not less than 5% andmore preferably not less than 9% with respect to a total amount of gasto be exhausted. In a case where oxygen is used as the reaction gas, inorder to avoid danger of explosion, it is necessary to supply oxygen inan amount which is not more than a critical oxygen concentration that isdetermined in accordance with a raw material carbon source to be used.In a case where a gas other than a gas containing oxygen atoms such asoxygen, ozone, or water is used as the reaction gas, it is morepreferable that the reaction gas have a volume fraction lower than 100%with respect to the total amount of gas. Further, it is possible to use,as the metal catalyst, nickel, ruthenium, palladium, or platinum. Thereaction gas may be diluted with an inert gas.

[Reaction Gas Injection Section 121]

The CNT production apparatus 100 includes a reaction gas injectionsection 121 for injecting the reaction gas described above. The reactiongas injection section 121 needs to be designed so that the reaction gasis exhausted without contacting a catalyst and a raw material gas whichhas not been used to synthesize CNTs but being mixed well with the rawmaterial gas which has been used to synthesize the CNTs (i.e., residualgas). For example, as in the present embodiment, the reaction gasinjection section 121 may be designed to inject the reaction gasdirectly to a space in which the residual gas exhausted from an exhaustsection 13 is collected and through which the residual gas is sent to anexhaust vent 15, i.e., a space divided by a surface of the exhaustsection 13. The reaction gas injection section 121 may include aplurality of reaction gas injection sections 121. In a case where amixed gas in which the residual gas and the reaction gas are mixed has ahigher temperature, a chemical reaction of the residual gas and thereaction gas further progresses. This makes it possible to preventgeneration of a carbon solid. Therefore, the reaction gas may be heatedin advance so as to have a high temperature.

[Exhaust Flow Volume Stabilization Section 120]

An exhaust flow volume stabilization section 120 is a device which isprovided to the pipe for leading, to the outside of the growth unit 10,gas having passed through the exhaust vent 15 and which is capable ofstabilizing, over time, a flow volume of exhaust from the pipe eventhough a carbon solid adheres to the pipe due to a long-time production.The exhaust flow volume stabilization section 120 includes at least (i)exhaust flow volume adjusting means 114 for adjusting an exhaust flowvolume in an exhaust pipe, and (ii) exhaust flow volume measuring means115 for measuring a flow volume of exhaust from the pipe. The exhaustflow volume stabilization section 120 may further include means such ascarbon solid adhesion prevention means 122 for preventing a carbon solidfrom adhering to the pipe.

The exhaust flow volume stabilization section 120 controls an exhaustflow volume by the exhaust flow volume adjusting means 114 so that avalue of the exhaust flow volume which value is measured by the exhaustflow measuring means 115 has an error falling within a range preferablyof ±20%, and more preferably of ±10%, relative to a central value, whichis a suitable exhaust flow volume preset for the pipe. This range isherein referred to as a “control range”. More specifically, first, theexhaust flow volume measuring means 115 calculates or measures, from,for example, a measured pressure difference and a measured exhausttemperature, an exhaust flow volume by, for example, carrying out acalculation process in accordance with a conversion formula. Then, in acase where the exhaust flow volume exceeds an upper limit of a presetcontrol range, exhaust flow volume controlling means (not illustrated)included in the exhaust flow volume adjusting means 114 lowers theexhaust flow volume by, for example, lowering a suction force of theexhaust flow volume adjusting means 114. In contrast, in a case wherethe exhaust flow volume falls below a lower limit of the control range,the exhaust flow volume controlling means carries out feedback controlso as to increase the exhaust flow volume by, for example, increasingthe suction force of the exhaust flow volume adjusting means 114. Notethat the feedback control may be carried out automatically or manually.This makes it possible to stably control a flow volume of exhaust froman exhaust vent.

[Exhaust Flow Volume Measuring Means 115]

The exhaust flow volume measuring means 115 is a device which isprovided to the pipe for leading, to the outside of the growth unit 10,gas having passed through the exhaust vent 15 and which is configured tomeasure an exhaust flow volume of gas to be exhausted after passingthrough the exhaust vent 15. For example, the exhaust flow volumemeasuring means 115 may have a function of measuring an exhaust flowvolume by measuring a pressure difference between at least two points inthe pipe which are apart from each other. It is more preferable that theexhaust flow volume measuring means 115 have a function of measuring agas temperature in the pipe. Specific examples of the exhaust flowvolume measuring means 115 include a differential pressure gauge formeasuring a pressure difference and a thermocouple for measuring a gastemperature. A pressure difference which can be measured with highaccuracy by use of a commercially-available differential pressure gaugeis, for example, 0.1 Pa or greater, and more preferably 1 Pa or greater.Therefore, it is preferable that two measurement points be sufficientlydistant from each other or a pressure loss section for causing ameasurable pressure loss be provided in a measurement zone between themeasurement points so that a pressure difference caused in themeasurement zone is, for example, 0.1 Pa or greater, and more preferably1 Pa or greater. Further, in order to improve flow volume measurementaccuracy, it is possible to increase the number of pressure measurementpoints to 3 or more. It may be impossible to accurately measure apressure difference if the pressure measurement points are too close indistance to each other. Hence, it is preferable that the pressuredifference be measured with an interval of 0.5D or more between thepressure measurement points assuming that D is an internal diameter ofan exhaust vent.

The pressure loss section may be any pressure loss member provided thatthe member can be provided in the pipe and can reduce a cross sectionalarea of the pipe. Examples of such a pressure loss member include anorifice plate, a Venturi tube, a nozzle, and a perforated panel.Commercially-available pressure loss members are normally in conformitywith predetermined standards (JIS Z 8762-1 through 4), and their shapesand measuring methods etc. are therefore standardized. In a case where apressure loss section in conformity with a standard is used, a flowvolume is calculated by using a calculation formula stipulated in thestandard. Note, however, that the calculation formula is only applicableto a condition that the pipe has an internal diameter of 50 mm or moreand a Reynolds number of 5,000 or more. A minimum required flow volumeestimated by the Reynolds number is approximately several hundred sLm.Therefore, the flow volume needs to be measured under conditions of anexhaust vent having a large diameter and a large exhaust volume.

It is preferable that the exhaust flow volume measuring means 115 use athermal fluid simulation. This is because the thermal fluid simulationmakes it possible to measure an exhaust flow volume with high accuracyeven under pipe diameter and flow volume conditions which are beyond thescope of application in a conventional method. For example, in a casewhere the pressure loss section is an orifice plate, a relationshipbetween a pressure difference to be lost ΔP and a flow volume F isrepresented by the following equation (2):

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 1} \right\rbrack & \; \\{F_{\lbrack{sLm}\rbrack} = \sqrt{\frac{\Delta \; P_{\lbrack{P\; a}\rbrack}}{\alpha}}} & (2)\end{matrix}$

where α is a function of a temperature, a density, and a viscosity of anexhaust gas. In a case where α is found based on a result of the thermalfluid simulation, it is possible to convert a pressure difference intoan exhaust flow volume with high accuracy. In a case where the thermalfluid simulation is used, the pressure loss section may have any shapeand a range of a measurable flow volume is not limited.

[Exhaust Flow Volume Adjusting Means 114]

The exhaust flow volume adjusting means 114 is a device which isprovided to the pipe for leading, to the outside of the growth unit 10,gas having passed through the exhaust vent 15 which is configured toadjust a flow volume of gas to be exhausted from the pipe. The exhaustflow volume adjusting means 114 has a function of adjusting a flowvolume of gas to be exhausted. Further, the exhaust flow volumeadjusting means 114 is capable of changing an exhaust flow volume in theexhaust vent 15 in accordance with a result measured by the exhaust flowvolume measuring means 115. Specific examples of the exhaust flow volumeadjusting means 114 include: gas suction devices for sucking gas such asa blower, a pump, and an ejector; and flow adjusting valves such as aball valve, a syringe valve, and a gate valve. In a case where theexhaust flow volume adjusting means 114 is means employing a method inwhich an ejector whose driving fluid is gas is used to control a suctionforce of the ejector by causing a mass flow controller to control a flowvolume of the driving fluid, it is possible to prevent a change inexhaust flow volume. Therefore, such means is more preferable to producean aligned CNT aggregate. Note that the gas is preferably air ornitrogen.

[Carbon Solid Adhesion Prevention Means 122]

The carbon solid adhesion prevention means is configured to prevent acarbon solid from adhering to a pipe by heating to and/or keeping at ahigh temperature a residual gas flowing in the pipe, the pipe leading,to an outside of the growth unit, gas having passed through a firstexhaust vent. According to the present embodiment, the carbon solidadhesion prevention means 122 is a device for heating to and/or keepingat a high temperature an inside of a portion of a pipe, which portioncorresponds to a zone in which a pressure difference is measured by theexhaust flow volume measuring means 115, so as to prevent a carbon solidfrom adhering to the portion of the pipe, the pipe leading, to anoutside of the growth unit 10, gas having passed through the exhaustvent 15. The exhaust flow volume stabilization section 120 including thecarbon solid adhesion prevention means 122 reduces a carbon solid thatadheres to the pipe in the portion. Therefore, it is possible to measurean accurate exhaust flow volume over a long time. This allows continuousproduction of aligned CNT aggregates to be stably maintained over alonger time.

Examples of the carbon solid adhesion prevention means 122 include aheater for heating the pipe and a heat insulating material for keepingthe pipe warm. A higher temperature of an exhaust gas further reduces anamount of a carbon solid that adheres to the pipe. It is preferable thecarbon solid adhesion prevention means 122 heat and/or keep warm anexhaust gas to and/or at a temperature of, for example, 150° C. orhigher, and more preferably of 300° C. or higher. Further, it ispreferable that the carbon solid adhesion prevention means 122 retain atemperature of the exhaust gas at 700° C. or lower. In a case where thetemperature of the exhaust gas is retained at 700° C. or lower, it ispossible to prevent problems (i) such that the pipe which is carburizeddeclines in strength and (ii) the pipe needs to be all-welded due todifficulty in use of a gas sealing method for a high-temperature gas.

[Cooling Unit 105]

The cooling unit 105 is a set of devices for carrying out a coolingstep, i.e., for cooling down the base substrate 111 on which an alignedCNT aggregate has grown. The cooling unit 105 has a function of coolingdown the aligned CNT aggregate and the base substrate 111 after thegrowth step.

The cooling unit 105 has a configuration in which a water-cooled typeand an air-cooled type are combined, and is constituted by the coolingfurnace 105 a in which an inert gas is retained, a coolant gas injectionsection 105 b that injects the inert gas into the cooling furnace 105 a,and a water-cooled cooling tube 105 c disposed to surround an internalspace of the cooling furnace 105 a. Note that the cooling unit may beconfigured to be of only the water-cooled type or the air-cooled type.

Cooling by the cooling unit 105 makes it possible to prevent oxidizationof the aligned CNT aggregate, a catalyst, and the base substrate 111after the growth step.

(Cooling Step)

A cooling step is a step of, after the growth step, cooling down thealigned CNT aggregate, the catalyst, and the base substrate in an inertgas. After the growth step, the aligned CNT aggregate, the catalyst, andthe base substrate are high in temperature, and therefore may beoxidized when placed in the presence of oxygen. This is prevented,during the cooling step, by cooling down the aligned CNT aggregate, thecatalyst, and the base substrate in the presence of the inert gas. Thetemperature during the cooling step is 400° C. or lower, more preferably200° C. or lower.

[Transfer Unit 107]

The transfer unit 107 is a set of devices necessary for continuouslytransferring a plurality of base substrates 111 to the CNT productionapparatus 100. The transfer unit 107 includes a mesh belt 107 a and abelt driving section 107 b. The transfer unit 107 transfers a basesubstrate 111 to each of furnace spaces in an order of the formationunit 102, the growth unit 10, and the cooling unit 105.

The transfer unit 107 is of a belt-conveyor type in which the basesubstrate 111 having a catalyst formed on a surface thereof istransferred out of the formation furnace 102 a into the cooling furnace105 a through the growth furnace 11. The transfer unit 107 transfers thebase substrate 111 by the mesh belt 107 a driven by the belt drivingsection 107 b, for example, with use of a reducer-equipped electricmotor. Moreover, the formation furnace 102 a and the growth furnace 11,and the growth furnace 11 and the cooling furnace 105 a have theirrespective internal spaces spatially connected via the connectionsections 109 and 110, respectively. This enables the mesh belt 107 a, onwhich the base substrate has been placed, to pass through the spacesbetween the respective furnaces.

Note that, in a case where the production apparatus of the presentinvention produces an aligned CNT aggregate continuously and includesthe transfer unit, a specific configuration of the transfer unit is notlimited to the above configuration. Examples of the transfer unitinclude a robot arm and a robot arm driving device in the case of amulti-chamber type.

[Connecting Sections 108 Through 110]

The connecting sections 108 through 110 are a set of devices via whichthe respective furnace spaces of the units are spatially connected andwhich serve to prevent the base substrate 111 from being exposed to theoutside air while the base substrate 111 is transferred from one unit toanother unit. Examples of the connecting sections 108 through 110include a furnace or chamber capable of shielding an environmentsurrounding the base substrate 111 from the outside air and passing thebase substrate 111 from one unit to another unit.

The inlet purge section 101 and the formation unit 102 are spatiallyconnected via the connecting section 108. The connecting section 108 isprovided with an exhaust section 103 a of the gas mixing preventionmeans 103, and through the exhaust section 103 a, a mixture of a purgegas injected from the inlet purge section 101 and a reducing gasinjected from the injection section 102 b is exhausted. This preventsthe purge gas from flowing into the formation furnace 102 a and thereducing gas from flowing in toward the inlet purge section 101.

The formation unit 102 and the growth unit 10 are spatially connectedvia the connecting section 109. The connecting section 109 is providedwith an exhaust section 103 b of the gas mixing prevention means 103,and through the exhaust section 103 b, a reducing gas inside of theformation furnace 102 a and a raw material gas and a catalyst activationmaterial inside of the growth furnace 11 are exhausted. This preventsthe raw material gas or the catalyst activation material from flowinginto the formation furnace 102 a and the reducing gas from flowing intothe growth furnace 11.

The growth unit 10 and the cooling unit 105 are spatially connected viathe connecting section 110. The connecting section 110 is provided withan exhaust section 103 c of the gas mixing prevention means 103, andthrough the exhaust section 103 c, a mixture of (i) a raw material gasand a catalyst activation material inside of the growth furnace 11 and(ii) an inert gas inside of the cooling furnace 105 a is exhausted. Thisprevents the raw material gas or the catalyst activation material fromflowing into the cooling furnace 105 a and the inert gas from flowinginto the growth furnace 11.

Note that the production apparatus of the present invention may furtherinclude heating means for heating the connecting section 110 between thegrowth unit 10 and the cooling unit 105. Note here that a decline intemperature in a place near an outlet of the growth furnace 11 may causea decomposition product from a raw material gas to be amorphous carbonand then to accumulate at a tip of a CNT. This may cause a CNT whichgrows in a vertical direction from a base substrate to have a tip-G/Dratio remarkably smaller than a root-G/D ratio.

However, in a case where the connecting section 110 between the growthunit 10 and the cooling unit 105 is heated, a difference between thetip-G/D ratio and the root-G/D ratio can be made smaller. Therefore, itis possible to obtain an aligned CNT aggregate with a stable quality.

Specific examples of the heating means may include heating means forheating a seal gas to be used in gas mixing prevention means (describedlater) which is included in the gas mixing prevention means 103 andlocated between the growth unit 10 and the cooling unit 105. It ispossible to heat the outlet of the growth furnace 11 and the place nearthe outlet by heating the seal gas.

[Gas Mixing Prevention Means 103]

The gas mixing prevention means 103 is a set of devices for carrying outa function of preventing gas from flowing out of a furnace space of oneof the units into that of another. The gas mixing prevention means 103is provided in the connecting sections 108 through 110 via whichrespective furnace spaces of the units are spatially connected. The gasmixing prevention means 103 includes the exhaust sections 103 a through103 c for exhausting, out of the system, gasses in the connectionsections 108 through 110 and/or respective places near the connectionsections 108 through 110.

Note that a configuration of the gas mixing prevention means 103 is notlimited to that of the present embodiment. However, the gas mixingprevention means 103 may be, for example, a gate valve device thatmechanically disconnects the spatial connection between one unit andanother during a period of time except when the base substrate 111 movesfrom one unit to another. Further, the gas mixing prevention means 103may be a gas curtain device that breaks the spatial connection betweenone unit to another by injecting an inert gas.

In order to surely prevent gas mixing, it is preferable that the gatevalve device and/or the gas curtain device be used in combination withan exhaust device. Further, from the viewpoint that CNTs are efficientlysynthesized by continuously transferring a base substrate from one unitto another, and in view of simplification of a production apparatus, itis more preferable that the exhaust device be used alone.

Further, the gas mixing prevention means of the present invention mayinclude (i) respective at least one seal gas injecting sections each ofwhich injects a seal gas along aperture planes of the inlets and theoutlets of the base substrate in the respective furnaces and (ii)respective at least one exhaust sections each of which exhausts the sealgas thus injected and other neighboring gases to an outside of theproduction apparatus mainly by sucking the seal gas so as to prevent theseal gas from entering the respective furnaces. In a case where the sealgas is injected along the aperture planes of the furnaces, it ispossible to block the inlets and outlets of the furnaces. This preventsthe gas outside the furnaces from flowing into the furnaces. Moreover,in a case where the seal gas is exhausted out of the productionapparatus, it is possible to prevent the seal gas from flowing into thefurnaces.

It is preferable that the seal gas be an inert gas. In particular, interms of safety, cost, etc., it is preferable that the seal gas benitrogen. The seal gas injection sections and the exhaust sections maybe provided so that one of the exhaust sections is located near acorresponding one of the seal gas injection sections or so that theexhaust sections face, across the mesh belt, the seal gas injectionsections, respectively. Note that it is preferable that the seal gasinjection sections and the exhaust sections be provided so that anoverall configuration of the gas mixing prevention means 103 issymmetrically located along a furnace length direction.

For example, it is preferable that two seal gas injection sections beprovided at respective both sides of one exhaust section so that theoverall configuration of the gas mixing prevention means has a structuresymmetrically located along the furnace length direction about a centerof the one exhaust section. Further, it is preferable that a total flowof gas injected from the seal gas injection sections and a total flow ofgas exhausted from the exhaust sections be substantially equal inamount. This makes it possible to (i) prevent gases which flow fromspaces on both sides of the respective gas mixing prevention means frommixing with each other and (ii) prevent the seal gas from flowing intothe spaces. In a case where the gas mixing prevention means are providedon both sides of the growth furnace, it is possible to prevent a flow ofthe seal gas and a flow of a gas in the growth furnace from interferingwith each other. Furthermore, turbulence in the flow of the gas due tothe flow of the seal gas into the growth furnace can be also prevented.Accordingly, it is possible to provide the production apparatus which issuitable for successively producing the aligned CNT aggregates.

Further, it is preferable that the gas mixing prevention means 103function so that the concentration of carbon atoms in an environment ofthe reducing gas in the formation furnace is kept smaller than or equalto 5×10²² atoms/m³, or more preferably smaller than or equal to 1×10²²atoms/ms.

Respective exhaust quantities Q of a plurality of exhaust sections,i.e., the exhaust sections 103 a through 103 c cannot be eachindependently determined, and need to be adjusted according to theamount of gas supplied to the whole apparatus such as the flow volume ofthe reducing gas, the flow volume of the raw material gas, and the flowvolume of a coolant gas. However, a necessary condition for gas mixingprevention to be satisfied can be represented by the following equation.

Q≥4DS/L

where D is the diffusion coefficient of a gas that needs to be preventedfrom flowing in, S is the sectional area of a boundary at which the gasis prevented from flowing in, and L is the length of each exhaustsection (along the length of the furnace). The exhaust quantity of eachof the exhaust sections 103 a through 103 c is set so that theconditional equation is satisfied and a balance between gas supply andgas exhaust in the whole apparatus is kept.

(Concentration of Carbon Atoms)

Inflow of a raw material gas into the formation furnace 102 a exerts aharmful influence on the growth of CNTs. It is preferable that theinflow of the raw material gas into the formation furnace 102 a beprevented by the gas mixing prevention means 103 so that theconcentration of carbon atoms in the environment of the reducing gas inthe formation furnace 102 a is kept smaller than or equal to 5×10²²atoms/m³, or more preferably smaller than or equal to 1×10²² atoms/m³.The “concentration of carbon atoms” here is calculated according to thefollowing equation (1):

$\begin{matrix}\left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack & \; \\{\left( {{Concentration}\mspace{14mu} {of}\mspace{14mu} {Carbon}\mspace{14mu} {Atoms}} \right) = {\sum\limits_{i}{C_{i}\frac{\rho_{i}D_{i}}{M_{i}}N_{A}}}} & (1)\end{matrix}$

where with respect to the types of gas contained in the environment ofthe reducing gas (i=1, 2, . . . ), the concentration (ppmv) is denotedby D₁, D₂, . . . , the density in standard condition (g/m³) is denotedby ρ₁, ρ₂, . . . , the molecular weight is denoted by M₁, M₂, . . . ,and the number of carbon atoms contained in each gas molecule is denotedby C₁, C₂, . . . , and the Avogadro's number is denoted by N_(A).

The production volume and quality of CNTs can be satisfactorilymaintained by keeping the concentration of carbon atoms in theenvironment of the reducing gas in the formation furnace 102 a at notgreater than 5×10²² atoms/m³. That is, the concentration of carbon atomsof 5×10²² atoms/m³ or smaller makes it possible, in the formation step,to satisfactorily exhibit the effects of reducing the catalyst,stimulating the catalyst to become fine particles suitable for thegrowth of CNTs, and improving the activity of the catalyst, whereby theproduction volume and quality of CNTs during the growth step can besatisfactorily maintained.

[Outlet Purge Section 106]

The production apparatus 100 has an outlet provided with the outletpurge section 106 which is substantially identical in configuration tothe inlet purge section 101. The outlet purge section 106 is a set ofdevices for preventing the outside air from flowing into the inside ofthe production apparatus 100 through the outlet for the base substrate111. The outlet purge section 106 has a function of causing theenvironment surrounding the base substrate 111 to be an environment of apurge gas.

The outlet purge section 106 injects a purge gas from up and down in theform of a shower and thereby prevents the outside air from flowing intothe cooling furnace 105 a through the outlet. Note that the outlet purgesection 106 may be constituted by a furnace or a chamber for maintainingthe environment of the purge gas and/or injection sections for injectingthe purge gas etc.

It is preferable that the purge gas be an inert gas. In particular, interms of safety, cost, and purging properties, it is preferable that thepurge gas be nitrogen.

In a case where the outlet for the base substrate 111 is always open,e.g., in a case where the transfer unit 107 is of a belt-conveyor typeas in the present embodiment, it is preferable that the outlet purgesection 106 have a structure such as the gas curtain structure asdescribed above. This configuration makes it possible to prevent theoutside air from flowing into the production apparatus 100 through theoutlet for the base substrate 111.

(Materials for Those Components of the Apparatus which are Exposed toEither the Reducing Gas or the Raw Material Gas)

Examples of those components of the apparatus which are exposed toeither the reducing gas or the raw material gas are the formation unit102, the growth unit 10, the transfer unit 107, the gas mixingprevention means 103, and some components of the connecting sections 108through 110. Specific examples include such components of the apparatusas the formation furnace 102 a, the injection section 102 b forinjecting a reducing gas, the growth furnace 11, the injection section12 for injecting a raw material gas, the mesh belt 107 a, the exhaustsections 103 a through 103 c of the gas mixing prevention means 103, andthe furnaces of the connecting sections 108 through 110.

Examples of materials for those components of the apparatus which areexposed to either the reducing gas or the raw material gas includematerials capable of resisting high temperatures, such as quartz,heat-resistant ceramic, and metals. The metals are preferable in termsof precision of processing, degree of freedom of processing, and cost.Examples of the metals include heat-resistant alloys. Examples of theheat-resistance alloys include heat-resistant steel, stainless steel,and nickel-based alloys. In general, heat-resistant steel refers tosteel that contains Fe in major proportions and other alloys inconcentrations of not more than 50%. Moreover, stainless steel refers tosteel that contains Fe in major proportions, other alloys inconcentrations of not more than 50%, and approximately not less than 12%of Cr. Further, examples of the nickel-based alloys include alloysobtained by adding Mo, Cr, Fe, and the like to Ni. Specifically, SUS310, Inconel 600, Inconel 601, Inconel 625, Incoloy 800, MC Alloy,Haynes 230 Alloy are preferable in terms of heat resistance, mechanicalstrength, chemical stability, and low cost.

In a case where the inner walls of the furnaces and/or components foruse in the furnaces are made of a metal, it is preferable that the metalbe a heat-resistant alloy and that a surface of the metal be plated withmolten aluminum or be polished so that the surface has an arithmeticaverage roughness Ra≤2 μm. This makes it possible to reduce carboncontaminants that adhere to the wall surfaces and the like when CNTs aresynthesized in a high-carbon environment. This favorably makes itpossible to prevent a decrease in production volume and deterioration inquality of aligned CNT aggregates.

(Molten Aluminum Plating)

Molten aluminum plating means a process of forming an aluminum oraluminum alloy layer on a surface of an object by dipping the objectinto a bath of molten aluminum. An example of the process is as follows:A preprocessing by washing a surface of a base metal (i.e., an object)and then dipping the object into a bath of molten aluminum atapproximately 700° C., thereby causing the molten aluminum to disperseinto the surface of the base metal, forming an alloy of the base metaland aluminum, and causing aluminum to adhere to the alloy layer when thebase metal is withdrawn from the bath. Furthermore, after the process, aprocess of exposing a Fe—Al alloy layer under the alumina and aluminumsurface layer by subjecting the surface layer to low-temperature thermaldiffusion may be executed.

(Polishing)

Examples of a method for polishing the heat-resistant alloy so that thearithmetic average roughness is Ra≤2 μm include: mechanical polishing,which is typified by buffing; chemical polishing, which involves the useof a chemical; electrolytic polishing, which is carried out whilepassing an electric current through an electrolyte; and complexelectrolytic polishing, which is a combination of mechanical polishingand electrolytic polishing.

(Arithmetic Average Roughness)

For a definition of arithmetic average roughness Ra, see “JIS B 0601:2001”.

As described above, in the production apparatus 100 according to thepresent embodiment, a series of the base substrates 111 each having acatalyst on a surface thereof is transferred by the transfer unit 107 topass through the inlet purge section 101, the formation unit 102, thegrowth unit 10, the cooling unit 105, and the outlet purge section 106in this order. In the meantime, the catalyst is reduced in anenvironment of the reducing gas in the formation unit 102, and CNTs growon the surfaces of the base substrates in an environment of the rawmaterial gas in the growth unit 10 and then is cooled down in thecooling unit 105.

The present invention is not limited to the description of the preferredembodiments above, but may be applied in many variations within thescope of gist thereof.

For example, through an appropriate setting of reaction conditions suchas raw material gas and heating temperature, it is possible toselectively produce either single-walled or multiwall CNTs, and it isalso possible to produce both single-walled and multiwall CNTs.

Further, according to the present embodiment, the catalyst is formedonto the surface of the base substrate by a film-forming apparatusprovided separately from the production apparatus. However, theproduction apparatus may be configured such that a catalyst film-formingunit is provided upstream of the formation unit 102 so that the basesubstrate passes through the catalyst film-forming apparatus before itpasses through the formation unit 102.

Further, according to the present embodiment, the formation unit 102,the growth unit 10, and the cooling unit 105 are arranged in this orderand have their respective furnace spaces spatially connected via theconnecting sections 108 through 110. However, a plurality of units thatprocess steps other than the formation step, the growth step, and thecooling step may be further provided somewhere and have their respectivefurnace spaces spatially connected via the connecting sections 108through 110.

Further, the present embodiment has discussed a case where the formationunit 102, the growth unit 10, and the cooling unit 105 are linearlyprovided. However, how to provide these units is not limited to this.The units may be circularly provided.

The above description has mainly discussed, as a suitable embodiment forcontinuously producing CNTs, an embodiment in which the formation unitand the growth unit are separately provided so that the base substrateis continuously transferred to each of these units. However, anembodiment of a production apparatus of the present invention is notlimited to such an embodiment. For example, the production apparatus maybe a batch type production apparatus in which a formation step and agrowth step are carried out in a single furnace. In this case, forexample, supply of a reducing gas required for the formation step can becarried out by, for example, an injection section of a growth unitincluded in the production apparatus of the present invention. Thisbrings about an advantage of forming a catalyst layer more uniformly onthe base substrate.

<Method for Producing Aligned Carbon Nanotube Aggregate>

A method of the present invention for producing an aligned carbonnanotube aggregate is a method for producing an aligned carbon nanotubeaggregate by synthesizing the aligned carbon nanotube aggregate on abase substrate that supports a catalyst on a surface thereof, the methodincluding: a growth step of synthesizing the aligned carbon nanotubeaggregate on the base substrate by supplying a raw material gas forcarbon nanotubes to the catalyst and heating at least either thecatalyst or the raw material gas, the growth step being carried out by agrowth unit, the growth unit including: at least one injection sectionincluding at least one injection hole from which the raw material gas isinjected to the base substrate; a first exhaust vent being on one side,relative to the at least one injection section, while a mounting surfaceon which the base substrate is placed is on the other side relative tothe injection section, for exhausting, out of a growth furnace, the rawmaterial gas that was injected from the at least one injection hole andthen contacted the base substrate, the growth furnace storing the basesubstrate while the aligned carbon nanotube aggregate is beingsynthesized; and an exhaust section including a plurality of secondexhaust vents that exhausts, towards the first exhaust vent, the rawmaterial gas that contacted the base substrate, the plurality of secondexhaust vents being provided so as to be closer to the first exhaustvent than a plurality of injection holes included in the at least oneinjection hole of the at least one injection section.

Descriptions of the growth step, the growth unit, the injection section,and the exhaust section are based on those given earlier of theapparatus for producing an aligned carbon nanotube aggregate inaccordance with the present invention.

The present invention is not limited to the descriptions of therespective embodiments, but may be altered within the scope of theclaims. An embodiment derived from a proper combination of technicalmeans disclosed in different embodiments is encompassed in the technicalscope of the invention.

As described above, the apparatus of the present invention for producingan aligned carbon nanotube aggregate is more preferably configured suchthat the exhaust section has a surface which faces the mounting surfaceand on which the plurality of second exhaust vents are provided.

A space is formed between the base substrate and the surface. It goeswithout saying that the space is smaller than the entire inner space ofa furnace in the case of the exhaust section having no surface. Thisreduces a region in which a raw material gas diffuses after being used.Further, in a case where a catalyst activation material is alsosupplied, a region is reduced in which the catalyst activation materialdiffuses after being used. The raw material gas that has been used isexhausted fast from the reduced region. This allows the raw material gasand/or the like that have/has been used to have a more uniformconcentration(s) in the space between the base substrate and theinjection section.

The apparatus of the present invention for producing an aligned carbonnanotube aggregate is more preferably configured such that the at leastone injection section has at least one injection hole row in which theplurality of injection holes are aligned.

This configuration allows the raw material gas to be injected to thebase substrate more uniformly.

The apparatus of the present invention for producing an aligned carbonnanotube aggregate is more preferably configured such that the at leastone injection hole row includes a plurality of injection hole rowsbetween adjacent ones of which a gap is formed.

A residual gas obtained after the raw material gas injected from theinjection holes is supplied to the base substrate and then reflectedfrom the base substrate passes through the gap fast and is removed froma space between the base substrate and the injection holes. Therefore,it is possible to more efficiently prevent the residual gas fromremaining in the space between the base substrate and the injectionholes, so that the raw material gas to be supplied to the base substratehas a more uniform concentration. Further, in a case where a catalystactivation material is also supplied, the catalyst activation materialalso has a more uniform concentration.

The apparatus of the present invention for producing an aligned carbonnanotube aggregate is more preferably configured such that at least oneof exhaust vent rows in which the plurality of second exhaust vents arealigned is located between adjacent ones of the injection hole rows.

In a case where the injection holes and the second exhaust vents areclose to each other, it is possible to exhaust faster, from the secondexhaust vents, the residual gas obtained after the raw material gasinjected from the injection holes is supplied to the base substrate andthen reflected from the base substrate. Therefore, it is possible tomore efficiently prevent the residual gas from remaining in the spacebetween the base substrate and the injection holes, so that the rawmaterial gas to be supplied to the base substrate has a more uniformconcentration. Further, in a case where a catalyst activation materialis also supplied, the catalyst activation material also has a moreuniform concentration.

The apparatus of the present invention for producing an aligned carbonnanotube aggregate is more preferably configured such that the at leastone injection section includes a plurality of injection hole rowsincluded in the at least one injection hole row in which the pluralityof injection holes are aligned, the plurality of injection hole rowsconstituting a comb-like pattern.

With this configuration, the raw material gas is supplied to the basesubstrate at a more uniform concentration. In a case where a catalystactivation material is also supplied to the base substrate, the catalystactivation material is also supplied to the base substrate at a moreuniform concentration. Therefore, it is possible to produce CNTs withmore uniform quality even in a case where a large area base substrate isused as the base substrate.

The apparatus of the present invention for producing an aligned carbonnanotube aggregate is more preferably configured such that the at leastone injection section includes two injection sections which face eachother so that a comb tooth of one of the two injection sections islocated between respective comb teeth of the other of the two injectionsections.

In a case where the raw material gas is supplied from the sections whichface each other, it is possible to further prevent unevenness intemperature and heating history of the raw material gas and consequentlyto supply, to the base substrate, the raw material gas which is moreuniform in temperature and heating history. Therefore, it is possible toproduce CNTs with more uniform quality.

The method for producing an aligned carbon nanotube aggregate inaccordance with the present invention is preferably arranged such thatthe supply of the raw material gas in the growth step includes supplyinga catalyst activation material. This makes it possible to maintain theactivity of the catalyst for a longer period of time.

EXAMPLES

The present invention is specifically described below with reference toExamples. However, the present invention is not limited to theseExamples.

[Base Substrate]

As a base substrate, a flat plate was used which had 500 mm in width×500mm in length, and 0.3 mm in thickness and was made of a Fe—Cr alloySUS430 (manufactured by JFE Steel Corporation, containing 18% Cr). Asurface roughness was measured at a plurality of points with use of alaser microscope and found to be an arithmetic average roughnessRa≈0.063 μm.

[Catalyst Formation]

A catalyst was formed on the base substrate by the following method.

1.9 g of aluminum tri-sec-butoxide was dissolved in 10 mL (78 g) of2-propanol, and then 0.9 g of triisopropanol amine was added as astabilizer and dissolved in a resulting mixture, so that a coating agentfor forming an alumina layer was prepared.

The base substrate was coated, by dip coating at a room temperature of25° C. and a relative humidity of 50%, with the coating agent forforming an alumina layer (described above). The coating was carried outunder the condition that the base substrate was dipped and then retainedfor 20 seconds, and was lifted at a speed of 10 mm/sec and thenair-dried for 5 minutes.

Subsequently, the base substrate was heated under an atmosphericenvironment at a temperature of 300° C. for 30 minutes and then cooleddown to a room temperature. An alumina layer having a film thickness of40 nm was thus formed as a carburization prevention layer on the basesubstrate.

Next, 174 mg of iron acetate was dissolved in 100 mL of 2-propanol, andthen 190 mg of triisopropanol amine was added as a stabilizer anddissolved in a resulting mixture, so that an iron layer coating agentwas prepared. The base substrate having the alumina layer thereon wascoated, by dip coating at a room temperature of 25° C. and a relativehumidity of 50%, with the iron layer coating agent. The coating wascarried out under the condition that the base substrate was dipped andthen retained for 20 seconds, and was lifted at a speed of 3 mm/sec andthen air-dried for 5 minutes. Subsequently, the base substrate washeated under an atmospheric environment at a temperature of 100° C. for30 minutes. After the heating, the base substrate was cooled down to aroom temperature, so that a catalyst layer having a film thickness of 3nm was formed.

Example 1

An aligned CNT aggregate was produced by causing the productionapparatus described in <Embodiment 1> to successively carry out aprocess including the formation step and the growth step.

An injection section included 20 injection hole rows which were providedat intervals of 200 mm and each of which (i) had a length of 500 mm and(ii) included 30 circular injection holes provided at regular intervalsand having a diameter of 5 mm. A distance between the base substrate andthe respective injection holes was set to 50 mm, and an angle formed byan injection axis line of each of the injection holes with a line normalto the base substrate was set to 0°.

An exhaust section included 20 exhaust vent rows which were provided atintervals of 200 mm and each of which (i) had a length of 500 mm and(ii) included 20 circular exhaust vents provided at regular intervalsand having a diameter of 15 mm. A distance between the base substrateand the respective exhaust vents was set to 150 mm.

The base substrate having a catalyst thereon was placed on a mesh beltof the production apparatus. An aligned CNT aggregate was produced onthe base substrate while a transfer speed of the mesh belt was beingchanged.

Conditions for each section of the production apparatus were set asshown in Table 1.

TABLE 1 GAS FLOW VOLUME FURNACE PROCESSING EXHAUST [sLm] TEMPERATURETIME QUANTITY COMPOSITION [° C.] [MIN] [sLm] INLET PURGE 300 SECTION 101N₂: 100% EXHAUST SECTION 100 100 103a N₂: 100% FORMATION UNIT 102 140820 28 140 H₂: 60% N₂: 40% EXHAUST SECTION 125 125 103b N₂: 100% GROWTHUNIT 10 150 810 11 150 C₂H₄: 10% H₂O: 100 ppm CO₂: 4% N₂: remainderEXHAUST SECTION 100 100 103c N₂: 100% COOLING UNIT 105  50 30 30 N₂:100% OUTLET PURGE 250 SECTION 106 N₂: 100%

Respective amounts of gasses to be injected from the reducing gasinjection section 102 b and the raw material gas injection section 12are set, in proportion to respective volumes of furnaces, to be suitableto produce an aligned CNT aggregate. Further, in order to securelyprevent a gas in the formation furnace 102 a from flowing into thegrowth unit 11 or a gas in the growth unit 11 from flowing into theformation furnace 102 a, the exhaust section 103 b was set to be thelargest in seal gas amount and exhaust quantity of the three exhaustsections 103 a, 103 b, and 103 c of the gas mixing prevention means 103.

Exhaust from the growth unit 10 was carried out while an exhaust flowvolume was being adjusted with use of the exhaust flow volumestabilization section 120 including the exhaust flow volume adjustingmeans 114 and the exhaust flow volume measuring means 115. The exhaustflow volume measuring means 115 was constituted by (i) an exhaust pipewhich has an inner diameter of 25 mm and includes two connecting pipesand one thermocouple insertion pipe, (ii) a pressure loss section madeof a circular plate (orifice plate) which has a thickness of 0.3 mm andhas, at its center, a hole having a diameter of 11 mm, (iii) a finepressure difference meter (Pressure Transducer DP 103 manufactured byValidyne Engineering Corporation) connected to each of the connectingpipes, and (iv) a sheath type thermocouple.

The exhaust flow volume adjusting means 114 was constituted by anejector, a driver gas cylinder, a massflow controller (exhaust flowvolume controlling means) for controlling a flow volume of a driver gas.An exhaust sucking force of the ejector was adjusted by using nitrogenas the driver gas and causing the massflow controller to control theflow volume of the driver gas.

The exhaust flow volume stabilization section 120 was used to control anexhaust flow volume of each of the sections so that a change over timein exhaust flow volume of the each of the sections falls within a rangeof ±10% during production of an aligned CNT aggregate.

Further, in order to reduce a carbon solid that adheres to an inside ofthe exhaust pipe, 40 sLm of hydrogen was injected as a reaction gas fromthe reaction gas injection section 121 and then exhausted through theexhaust vent 15 while being mixed with an exhaust gas (residual gas)from the growth unit.

Example 2

An aligned CNT aggregate was produced by causing the productionapparatus described in <Embodiment 2> to successively carry out aprocess including the formation step and the growth step.

An injection section included 20 injection hole rows which were providedat intervals of 200 mm and each of which (i) had a length of 500 mm and(ii) included 30 circular injection holes provided at regular intervalsand having a diameter of 5 mm. A distance between the base substrate andthe respective injection holes was set to 50 mm, and an angle formed byan injection axis line of each of the injection holes with a line normalto the base substrate was set to 0°.

An exhaust section included 20 exhaust vent rows which were provided atintervals of 200 mm and each of which (i) had a length of 500 mm and(ii) included 20 circular exhaust vents provided at regular intervalsand having a diameter of 15 mm. A distance between the base substrateand the respective exhaust vents was set to 150 mm.

The base substrate having a catalyst thereon was placed on a mesh beltof the production apparatus. An aligned CNT aggregate was produced onthe base substrate while a transfer speed of the mesh belt was beingchanged. Conditions for each section of the production apparatus wereset similar to those of Example 1.

Example 3

An aligned CNT aggregate was produced by causing the productionapparatus described in <Embodiment 3> to successively carry out aprocess including the formation step and the growth step.

An injection section included 20 injection hole rows which were providedat intervals of 200 mm and each of which (i) had a length of 500 mm and(ii) included 30 circular injection holes provided at regular intervalsand having a diameter of 5 mm. A distance between the base substrate andthe respective injection holes was set to 50 mm, and an angle formed byan injection axis line of each of the injection holes with a line normalto the base substrate was set to 0°.

An exhaust section included 20 exhaust vent rows which were provided atintervals of 200 mm and each of which (i) had a length of 500 mm and(ii) included 20 circular exhaust vents provided at regular intervalsand having a diameter of 15 mm. A distance between the base substrateand the respective exhaust vents was set to 150 mm.

The base substrate having a catalyst thereon was placed on a mesh beltof the production apparatus. An aligned CNT aggregate was produced onthe base substrate while a transfer speed of the mesh belt was beingchanged. Conditions for each section of the production apparatus wereset similar to those of Example 1.

[Comparison of Produced Aligned CNT Aggregates]

Uniformity of the aligned CNT aggregates produced by the productionapparatuses of the present invention was evaluated by measuring adistribution of G/D ratios. A raman spectrum of the aligned CNTaggregates was measured by using a microlaser raman system (Raman RXN1Analyzer 532 manufactured by Kaiser Optical Systems, Inc.) andirradiating a surface of the aligned CNT aggregates with a laser beamhaving a wavelength of 532 nm. The measurement was carried out at 25points which are arranged on the surface in a grid pattern so that 5points are arranged at regular intervals in each of vertical andhorizontal directions of the surface having a size of 500 mm×500 mm.FIGS. 7 through 12 show distributions of G/D ratios of the aligned CNTaggregates produced in Examples 1 through 3.

Examples 1 through 3 each made it possible to obtain, at any point on abase substrate, a CNT having a high G/D ratio. According to Examples 1and 2, there is a slight gradient in the distributions of the G/D ratiosdue to a temperature of a raw material gas and a heating history.Meanwhile, according to Example 3, there is a less steep gradient in thedistributions of the G/D ratios.

Further, the aligned CNT aggregates produced in each of the Examples 1through 3 of the present invention had the other properties of: a weightper base substrate area of 1.7 to 1.8 mg/cm², a density of 0.025 to 0.03g/cm³, an average external diameter of 2.8 to 3.0 nm (half width: 2 nm),a carbon purity of 99.9%, a Hellman's orientation coefficient of 0.7,and an average specific surface area, measured based on a BET methodwith use of a BET specific area measuring apparatus (HM model-1210manufactured by MOUNTECH Co., Ltd.), of 1100 to 1200 m²/g.

INDUSTRIAL APPLICABILITY

An aligned CNT aggregate obtained by the production method in accordancewith the present invention is suitably usable in fields of, for example,electronic device materials, optical element materials, and conductivematerials.

REFERENCE SIGNS LIST

-   -   10, 20, 30 Growth Unit    -   11 Growth Furnace    -   12, 32′, 32″ Injection Section    -   12 a Injection Hole    -   13 Exhaust Section    -   13 a Exhaust Vent (Second Exhaust Vent)    -   14 Mounting Surface    -   15 Exhaust Vent (First Exhaust Vent)    -   100 CNT Production Apparatus (Apparatus for producing an aligned        carbon nanotube aggregate)    -   111 Base Substrate

1. An apparatus for producing an aligned carbon nanotube aggregate bysynthesizing the aligned carbon nanotube aggregate on a base substratethat supports a catalyst on a surface thereof, the apparatus comprising:a growth unit for synthesizing the aligned carbon nanotube aggregate onthe base substrate by supplying a raw material gas for carbon nanotubesto the catalyst and heating at least either the catalyst or the rawmaterial gas, the growth unit including: at least one injection sectionincluding at least one injection hole from which the raw material gas isinjected to the base substrate; a first exhaust vent being on one side,relative to the at least one injection section, while a mounting surfaceon which the base substrate is placed is on the other side relative tothe injection section, for exhausting, out of a growth furnace, the rawmaterial gas that was injected from the at least one injection hole andthen contacted the base substrate, the growth furnace storing the basesubstrate while the aligned carbon nanotube aggregate is beingsynthesized; and an exhaust section including a plurality of secondexhaust vents that exhausts, towards the first exhaust vent, the rawmaterial gas that contacted the base substrate, the plurality of secondexhaust vents being provided so as to be closer to the first exhaustvent than a plurality of injection holes included in the at least oneinjection hole of the at least one injection section.
 2. The apparatusas set forth in claim 1, wherein the exhaust section has a surface whichfaces the mounting surface and on which the plurality of second exhaustvents are provided.
 3. The apparatus as set forth in claim 1, whereinthe at least one injection section has at least one injection hole rowin which the plurality of injection holes are aligned.
 4. The apparatusas set forth in claim 3, wherein the at least one injection hole rowincludes a plurality of injection hole rows between adjacent ones ofwhich a gap is formed.
 5. The apparatus as set forth in claim 3, whereinat least one of exhaust vent rows in which the plurality of secondexhaust vents are aligned is located between adjacent ones of theinjection hole rows.
 6. The apparatus as set forth in claim 3, whereinthe at least one injection section includes a plurality of injectionhole rows included in the at least one injection hole row in which theplurality of injection holes are aligned, the plurality of injectionhole rows constituting a comb-like pattern.
 7. The apparatus as setforth in claim 6, wherein the at least one injection section includestwo injection sections which face each other so that a comb tooth of oneof the two injection sections is located between respective comb teethof the other of the two injection sections.